A closer look at different territorial behavior among the birds

Why do I only have one or two cardinals at a time at the feeder and like a dozen finches visiting at once? ~ Lansing

That is an excellent observation. It has a lot to do with food availability and guarding nesting territories.  A “territory” can be defined as any defended area, even if it's just during nesting. Defending a territory requires time & energy but the benefits may include improved access to resources like food and nest sites.

As many of you have noticed in the spring, Northern Cardinals become very aggressive towards other cardinals or even their reflections in the window, in order to claim the perfect nesting territory and ample foraging areas for a potential mate.

For American Goldfinches, once a male has found a mate, he selects a territory, marking the boundaries by warbling as he flies from perch to perch. However, two or three pairs of finches may group their territories close together to form a loose colony.

About 13% of bird species exhibit colonial nesting. The advantages of this may be many more eyes available to detect and aid in defense of predators and exchanging information on the best foraging areas. The disadvantages include increased competition for mates, nesting areas, and food.  And large groups may attract predators and facilitate the spread of parasites and diseases.

Birds have learned different ways to survive. Whether to defend territories against other birds of the same species or to allow the formation of colonies depends on if the benefits of defense outweigh the costs. Once nesting is completed most birds like to gather in larger flocks for protection and to forage. Many people report having several pair of cardinals on their feeder by Thanksgiving and double the amount of flocking finches too.

Source: Territoriality & Coloniality

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